Light Curing Cyanoacrylates: Breakthrough Technology for Medical Device Assembly
This article is based on an original publication by Loctite.
Developed in 1999, light cure cyanoacrylate (UVCA) adhesives were created to provide all the advantages of cyanoacrylates and light cure adhesives without the limitations. Engineered to offer an immediate surface cure when exposed to low intensity light, this revolutionary technology cures in shadowed areas via a unique reaction with surface moisture.
Designed to provide tack-free fixture within seconds of low intensity ultraviolet light exposure, UVCAs are one-part and solvent-free. Uninhibited by oxygen, the adhesive forms a dry, glassy surface with even minimal light source exposure.
Tack-free cure is essential when an adhesive is used as a coating in device applications or when excess adhesive is inevitable. Even UVCA adhesives applied in shadowed areas cure quickly at room temperature due to a secondary moisture cure mechanism, and fillets of adhesive take only seconds to cure with exposure to low intensity light. Fast cure times prevent blooming and frosting without the need for accelerators.
UVCA adhesives deliver a range of high-speed assembly performance benefits. Fast and reliable, these adhesives process quickly and cure rapidly without heat or racking of parts. Based on cyanoacrylate chemistry, UVCAs offer high bond strength for a range of substrates to deliver enhanced performance with a guaranteed complete cure.
Processing: Dispensing and Curing UVCAs
There are two light cure cyanoacrylate variations currently available: low viscosity (20 cP) and high viscosity (900 cP) variations, which allow materials to be dispensed in various ways. For instance, manual dispense methods allow the adhesive to be applied directly from small packages to the device in moderate production quantities. Pressure-time and positive displacement dispense systems ensure consistent quality for semi- and fully-automated production applications.
Cyanoacrylate-based UVCAs are subject to the same challenges as their parent technology, and device manufacturers must therefore carefully consider dispenser type and method to avoid premature cure or accelerated aging. Using low intensity light sources to ensure a full cure, UVCAs produce a lower overall capital expenditure.
The improved cure through depth of UVCAs makes them ideal for applications such as filling large bond areas in fluid collection device housings, or potting of surgical monitoring device connectors and bodies. UVCAs prevent stress cracks while allowing an adhesive cure to depths of more than 0.25 inch in less than 15 seconds.
Typically dependent on the substrate, fixture time for the adhesive’s secondary shadow cure can vary from seconds to several minutes. Shadowed areas require adequate surface moisture with relative humidity levels of 40 to 60 percent to achieve a full cure within approximately 24 hours.
Typical Performance Data
Often used for plastic disposable device assembly, light cure acrylics and cyanoacrylates provide unusually high bond strength to plastics.
Approximate Shear Strength (in PSI)